The present disclosure relates to compounds, e.g., multisubstituted aromatic compounds, which exhibit biological activity, e.g., inhibitory action, against thrombin (activated blood-coagulation factor II; EC 3.4.21.5).
In mammalian systems, blood vessel injuries result in bleeding events, which are dealt with by the blood coagulation cascade. The cascade includes the Extrinsic and Intrinsic pathways, involving the activation of at least 13 interconnected factors and a variety of co-factors and other regulatory proteins. Upon vascular injury, plasma factor VII interacts with exposed Tissue Factor (TF), and the resultant TF-fVIIa complex initiates a complex series of events. Factor fXa is produced directly ‘downstream’ from the TF-fVIIa complex, and amplified manifold via the Intrinsic Pathway. FXa then serves as the catalyst for formation of thrombin (fIIa), which in turn is the direct precursor to fibrinolysis. The outcome is a fibrinolytic clot, which stops the bleeding. Fibrinolysis of the polymeric clot into fibrin monomers leads to dissolution and a return of the system to the pre-clot state. The cascade is a complex balance of factors and co-factors and is tightly regulated.
In disease states, undesired up- or down-regulation of any factor leads to conditions such as bleeding or thrombosis. Historically, anticoagulants have been used in patients at risk of suffering from thrombotic complications, such as angina, stroke and heart attack.
Warfarin has enjoyed dominance as a first-in-line anticoagulant therapeutic. Developed in the 1940s, it is a Vitamin K antagonist and inhibits factors II, VII, IX and X, amongst others. It is administered orally, but its ease of use is tempered by other effects: it has a very long half life (>2 days) and has serious drug-drug interactions. Importantly, since Vitamin K is a ubiquitous cofactor within the coagulation cascade, antagonism results in the simultaneous inhibition of many clotting factors and thus can lead to significant bleeding complications.
Much attention has been focused on heparin, the naturally-occurring polysaccharide that activates AT III, the endogenous inhibitor of many of the factors in the coagulation cascade. The need for parenteral administration for the heparin-derived therapeutics, and the inconvenient requirements for close supervision for the orally available warfarin, has resulted in a drive to discover and develop orally available drugs with wide therapeutic windows for safety and efficacy.
Indeed, the position of thrombin in the coagulation cascade has made it a popular target for drug discovery. Without wishing to be bound by any theory, it is believed that the ultimate development of direct thrombin inhibitors (DTIs) is usefully based upon the classical D-Phe-Pro-Arg motif, a sequence that mimics fibrinogen, which is a natural substrate of thrombin. Without further wishing to be bound by any theory, it is believed that the use of DTIs is very well precedented, such as with the hirudin-based anticoagulants, and thus there is strong interest in the discovery and development of novel DTIs.
A thorough discussion of thrombin and its roles in the coagulation process can be found in a variety of references, including the following which are incorporated herein by reference in their entireties and for all purposes: Wieland, H. A., et al., 2003, Curr Opin Investig Drugs, 4:264-71; Gross, P. L. & Weitz, J. I., 2008, Arterioscler Thromb Vasc Biol, 28:380-6; Hirsh, J., et al., 2005, Blood, 105:453-63; Prezelj, A., et al., 2007, Curr Pharm Des, 13:287-312.